Existing battery capacity measurement approaches suffer one or more of the following disadvantages:    1. Being off line approaches, so that continuity of monitoring is interrupted.    2. Requiring full discharge that leaves other equipment vulnerable and exposed to shutdown.    3. Requiring sophisticated and expensive testing equipment.    4. Requiring manual operation for performing the measurement.    5. Requiring special AC/DC converter rectification noise level similar to that available with UPS's.    6. Inaccuracy.
In consequence the existing battery capacity measurement techniques are either not acceptable to the telecommunications community because they leave a system vulnerable to failure, demand high cost, impose long delays between testing, require manual measurement procedure, or are not allowed due to telecommunications standards (as is the case with rectification noise levels).
A full discharge test into a stable load is recommended by industry and professional institutions as the only reliable approach for battery capacity measurement and is often referred to as the “capacity test”. This approach, however, suffers from substantial disadvantages including the requirement of bulky external loads, the need for backup power supplies, and the labour required to set up and supervise the procedure.
Lately impedance/conductance techniques have become popular for obtaining estimates of battery capacity. These techniques require the use of specialised equipment. In addition there is some uncertainty surrounding their effectiveness with most of the researchers dealing with these techniques being reluctant to promote them as a replacement to the “capacity test”.
Due to the dependence of battery capacity on the operating parameters of temperature and discharge rate the accuracy of other existing techniques is not acceptable. Accumulation type techniques depend on an estimation of charging efficiency and require correction factors for different discharge temperatures and rates. In addition they are not tolerant to disruptions to their short term data history.
Curve fitting and parametric models are two other common approaches which also suffer from the requirement of correction factors for different discharge temperature and rates. Curve fitting models try to match the discharge voltage versus time curve to either an exponential parabolic or hyperbolic curve. Some models employ more complex hybrid approaches. The major disadvantage with these models is that for each combination of discharge conditions and battery type a parameter set is required. These parameter sets are obtained through an exhaustive series of discharge tests. Parametric models are based on internal battery parameters such as internal resistance. Models such as this estimate SOC (state of charge) or reserve time by redrawing the manufacturers discharge voltage time curves based on the change in internal resistance. Battery resistance, however, is not always supplied by the manufacturer and therefore must be measured.
The present invention seeks to provide a method by which at least some of the aforedescribed disadvantages are mitigated or overcome. It seeks to provide a method which at the least provides information concerning the capacity of one battery relative to that of another battery, and/or the capacity as influenced by the operating conditions and optionally additionally or alternatively information concerning the absolute or intrinsic charge capacity of a battery.